In a high bandwidth communications system where the communications nodes are in motion relative to earth-based subscriber units, a subscriber unit typically maintains a link with the moving communications node using a narrow communications beam. A narrow communications beam allows the earth-based subscriber unit to transmit information to and receive information from the moving communications node at high data rates. Typically, a more narrow receive or transmit beam allows a higher data rate to be used between the communications node and the earth-based subscriber.
Previous earth-based systems used for tracking moving communications nodes, such as low earth orbit satellites, involve the use of mechanically steered reflector antennas. However, when the communications node is a low earth orbit satellite, the satellite may travel from one horizon to another and be in view of the subscriber unit for only a few short minutes. Therefore, since the mechanically steered reflector antenna must constantly be moved in order to maintain the communications link between the satellite and the subscriber unit, the mechanical components begin to wear and must periodically be replaced. This periodic replacement increases the life cycle cost which an earth-based subscriber must pay in order to receive and transmit high-bandwidth information to and from a moving satellite communications node.
Some other techniques for maintaining a communications link with a moving communications node involve the use of two-dimensional electronically scanned antenna arrays through the use of a digital beamformer. In a two-dimensional array which uses a digital beamformer, each transmit antenna element incorporates an individual power amplifier. Additionally, each receive element incorporates an individual low noise amplifier. The need for individual amplification of both receive and transmit antenna elements, as well as the need to perform a large number of digital operations in the beamformer itself, as well as the need for interconnections between the beamformer and the array of antenna elements involves substantial complexity in the required electronics and is therefore cost prohibitive for use by individual earth-based subscribers.
Therefore, what is desirable, is a low-cost system with minimal moving parts to provide beam steering in the communications antenna of the subscriber unit. A low-cost beam steering communications antenna using fewer moving parts also increases the reliability of the antenna over complex mechanically steered systems. These features make communications with a moving satellite accessible to a greater number of users with increased reliability.